The principal objective of this study is to test the non-nutritive character of dietary fiber and the infuence of fiber on fecal composition in humans. Two dietary sources of fiber, wheat bran and brussel sprouts are to be compared in digestion balance, and the bioavailablity of minerals, water soluble vitamins measured and also the digestibility of the two fiber sources in an 81 day experiment with 12 male human subjects. The biological degradability of cereal and vegetable fibers by human fecal bacteria; rumen bacteria and cellulase enzymes will be compared and the capacity of fecal and rumen cultures to alter potential carcinogenic substances measured in vitro. The problem of fiber determination will be investigated by comparing the chemical composition and physical properties of cereal, vegetable and fecal fiber and to use these observations to compare the validity of various methods for determination of food fiber, including AOAC crude fiber, detergent fibers and non-nutritive residues. The recovery of plant cell wall components, cellulose, hemicellulose, lignin and pectin and foreign matter in the residue obtained by the digestive methods will be determined. Transit measurements will be made with particulate and liquid markers to test the effect of fibers upon transit time, capacity, and surface exchange properties as well as the characteristics of various markers.